P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\titulka.jpg PV204 Security technologies Trusted boot •Petr Švenda svenda@fi.muni.cz •Faculty of Informatics, Masaryk University P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Overview •Booting chain of programs •BIOS as root of trust •Verified and Measured boot •Trusted boot in the wild –Trusted Platform Module –Chromium, Windows 8/10, UEFI… •Dynamic root of trust –Intel’s TXT, SGX • • • | PV204: Trusted boot 2 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Motivation – untrusted host platform •Traditional role of operating system –Isolate processed –Manage privileges, authorize operations •But how to deal with –Debugger, disassembler –Intercepted multimedia output –Malware run along with banking app –Keyloggers, Evil maid –System administrators, Service providers –… – • • | PV204: Trusted boot D:\Documents\Obrazky\question.png 3 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Solution? •Code signing (e.g., Microsoft AuthentiCode) –Application binary is signed, PKI used to verify certificate –If not signed, user is notified –Mandatory signing for selected applications (drivers…) – – – – – – – – | PV204: Trusted boot Signed == Secure? D:\Documents\Obrazky\question.png 4 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Trust in program’s functionality •Trust in a program’s code? –Signed code can still contain bugs and vulnerabilities •Trust only in a program’s code? –Underlying OS layers –Underlying firmware –Underlying hardware –Memory used by the program –Other code with access to the program’s memory/code –… •The program is almost never executed “alone” | PV204: Trusted boot 5 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Problem statement •How to make sure that valid programs run only within valid environment? • 1.Is possible to start valid environment on previously compromised machine? 2.Is possible to prevent tampering of apps against attacker with physical access? 3.How to prove to remote party what apps are running on local machine? | PV204: Trusted boot 6 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Classical boot chain | PV204: Trusted boot http://www.thegeekstuff.com/2011/02/linux-boot-process/ http://social.technet.microsoft.com/wiki/contents/articles/11341.the-windows-7-boot-process-sbsl.as px Linux Windows (7) How to detect that BIOS or OS Loader was modified? (evil maid, bootkit…) D:\Documents\Obrazky\question.png 7 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg How to arrive at expected chain of apps? 1.Just trust the whole boot process 2.Make all applications in protected read-only memory –If read-only => cannot be updated. Is it really what is running? 3.Signature-based approach: “Verified boot” –Before next app is executed, its signature is verified –Requires valid (unforged) public key (integrity) –Requires trust to owner of private key (signs only valid applications) 4.Create un-spoofable log what executed: “Measured” boot –Before next app is executed, its hash (“measurement”) is computed added to un-spoofable log (TPM’s PCR) –Will NOT prevent run of unwanted app, but environment cannot lie about what was executed (after-the-fact examination) –Requires (protected) log storage (Trusted Platform Module) –May require authentication of log (Remote attestation) | PV204: Trusted boot 8 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg “Verified” boot (signatures) | PV204: Trusted boot •“Measured” boot •(cumulative hash) •Trusted boot 9 > P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg “Verified” boot • | PV204: Trusted boot BIOS MBR GRUB Kernel User app … VERIFY (RSA) VERIFY (RSA) VERIFY (RSA) VERIFY (RSA) MEASURE: PCR = H(PCR | H(MBR)) MEASURE: PCR = H(PCR | H(GRUB)) MEASURE: PCR = H(PCR | H(Kernel)) MEASURE: PCR = H(PCR | H(User app)) •Nothing => BIOS is Root of Trust What verifies or measures BIOS? D:\Documents\Obrazky\question.png RESET: PCR = 0 PCR = H(…H(H(0|H(MBR))|H(GRUB)…H(User app)) •“Measured” boot 10 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Root of trust (for verified/measured boot) •Verified and Measured boot need some root of trust –Initial piece of code that nobody verifies/measures •Static root of trust –Start building trusted chain after reset of whole device •Dynamic root of trust –Start building trusted chain without reset of device (faster) •What can be root of trust? –static root of trust: BIOS, UEFI firmware, Intel Boot Guard –dynamic root of trust: Intel TXT, Intel SGX •Root of trust requires special protection –As nobody verifies than nobody will detect eventual modification – | PV204: Trusted boot 11 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg BIOS as root of trust •First code executed on CPU of target machine •Privileged access to hardware –E.g., can write into memory of OS code via DMA •Provides code for System Management Mode (SMM) –Routines executed during the whole platform runtime –x86 feature since 386, all normal execution is suspended –Used for power management, memory errors, hardware-assisted debugger… –Very powerful mode (=> also target of “ring -2” rootkits) – | PV204: Trusted boot 12 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg BIOS – security considerations •How BIOS verifies integrity of next module to run? •Where public key(s) for verification are stored? •How to handle updates of signing keys? •How BIOS checks signatures on its own updates? •How BIOS can be compromised? • | PV204: Trusted boot D:\Documents\Obrazky\question.png 13 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg How BIOS can be compromised? 1.Maliciously written by BIOS vendor (backdoor) 2.Replacement of genuine BIOS by malicious one –By physical flash (SPI programmer) of BIOS code –By lack of flashing protection mechanism by original BIOS –By code logic flaws in BIOS locking mechanisms 3.Modification of other code/data used by BIOS –Bug in parsing unsigned data… •Currently used protections: –Chipset-enforced protection of flash memory with BIOS –BIOS signature verification before new version is written –Hardware-aided check of executed code (TPM, TXT, SGX) –Check of BIOS signature before execution by CPU (IBG) – | PV204: Trusted boot 14 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg BIOS write locking – “locks” •Prevent unauthorized BIOS flash (from host OS) •Allow for authorized BIOS changes –BIOS upgrade, signing keys update –Change of persistent configurations (boot device…) •Locking mechanism (locks) for BIOS memory write 1.Locks are unlocked after reboot 2.Signature on new BIOS version is verified by old BIOS, and new is flashed eventually (before locking locks) 3.BIOS configuration (boot device priority) is written before locking locks 4.Locks locked before handling execution to other code 5. | PV204: Trusted boot 15 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Attacks against BIOS locks 1.Attacks typically via BIOS code vulnerability –BIOS usually does not takes (much) user input, but parsing of BIOS update blob, parts are unsigned (logo) –Buffer overflow in logo parsing => Locks are not locked yet => write own BIOS –http://invisiblethingslab.com/resources/bh09usa/Attacking%20Intel%20BIOS.pdf 2.Write into flash memory by SPI programmer – | PV204: Trusted boot Which one is more serious? Different attacker models 1. Is remote, but patchable 2. Is local attacker, but requires design changes to prevent D:\Documents\Obrazky\question.png 16 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Impact: Attack against Tails live-CD distro •Tails is live-CD Linux distribution •Designed to provide security even on previously compromised computer –Boot complete fresh OS from live-CD + security tools •Attack 1: Physical BIOS modification –Modified BIOS inserts malicious code into Tails during boot time –Known thread, physical access to computer assumed •Attack 2: SMM rootkit (LightEater) –Bug in BIOS exploited by remote party to modify SMM routines •Main issue: Tails tries to start with clean erased computer, but some elements still persist erase (BIOS modifications) | PV204: Trusted boot 17 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg INTEL BOOT GUARD (IBG) • | PV204: Trusted boot 18 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Intel Boot Guard (IBG) •Recently (2014) introduced feature to protect BIOS –Piece of trusted processor-provided, ROM-based code –Runs first after reset, verifies Initial Boot Block (IBB) 1.“Measured” boot mode (TPM-based) –Passively extends TPM’s PCRs by hash of IBB 2.“Verified” boot mode (digital signature) –OEM vendor hardcodes public key via fuses into CPU –Intel Boot Guard checks signature of IBB by OEM’s key –Only vendor-approved IBB=>BIOS=>OS is executed 3.Combination of measured and verified mode | PV204: Trusted boot 19 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg BIOS Intel Boot Guard – new root of trust • | PV204: Trusted boot BIOS MBR GRUB Kernel User app … Intel Boot Guard (CPU) VERIFY (RSA) VERIFY (RSA) VERIFY (RSA) VERIFY (RSA) VERIFY (RSA) MEASURE: PCR = H(BIOS-IBB) MEASURE: PCR = H(PCR | H(MBR)) MEASURE: PCR = H(PCR | H(GRUB)) MEASURE: PCR = H(PCR | H(Kernel)) MEASURE: PCR = H(PCR | H(User app)) IBG: Measured mode IBG: Verified mode 20 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Intel Boot Guard – security improvements •What attacks are mitigated by Intel Boot Guard? •Direct BIOS flash by SPI programmer –Mitigated, signature/measurement mismatch •Remote change of BIOS / BIOS data –Mitigated, signature/measurement mismatch •Other bug in BIOS code –Not mitigated, signed code still contains bug – •Any new attacks opened by IBG? | PV204: Trusted boot 21 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg How hard is to incorporate backdoor? •OEM vendor can sign backdoored BIOS –But multiple OEM vendors exist, open-source coreboot •Intel Boot Guard is written by Intel only –But OEM fuses own verification public key, right? –But it is the IBG code that actually verifies •Trivial backdoor (inside IBG code inside CPU) –if (IBB[SOME_OFFSET] == BACKDOOR_MAGIC) then always load provided BIOS (no signature check) –Or possibly verify by some other public key (secure even when BACKDOOR_MAGIC is leaked) | PV204: Trusted boot 22 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Short summary •Signature-based “verified” boot approach –Whitelisting approach – run only what is signed –Robust signature process needed (trust in private key owner) –Integrity of verification public key is critical –Key management is necessary (multiple keys, key updates) •“Measured” boot approach –Un-spoofable log of hashes of executed code –Can be remotely verified (remote attestation, explained later) •Root of trust needs to be protected –Historically was BIOS (+ update signatures + write locks) –Recently Intel Boot Guard inside CPU (signature of BIOS) | PV204: Trusted boot 23 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg TRUSTED PLATFORM MODULE • | PV204: Trusted boot 24 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg TPM hardware •Cryptographic smart card connected/inside to device –Secure storage, secure crypto environment… –(But not programmable JavaCard J) •Physical placement 1.Additional chip on motherboard 2.Incorporated inside CPU 3.Incorporated in peripheral (Ethernet card) •Accessed during boot time –“Measured” boot (TPM’s PCR registers) –Bitlocker encrypted drive keys •Accessed later (private key operation) | PV204: Trusted boot D:\Documents\Obrázky\TPM_Asus.jpg 25 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Trusted platform module • | PV204: Trusted boot D:\Documents\Obrázky\TPM.svg.png Author: Guillaume Piolle 26 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Trusted Platform Module (TPM) •ISO/IEC 11889 standard for secure crypto-processor •Versions published by Trusted Computing Group –https://trustedcomputinggroup.org –TPM 1.2 (2011) –TPM 2.0 (2016, not compatible with 1.2, but downgrade switch) •Tools to communicate with TPM –Windows: Microsoft PCPTool, TSS.MSR, Windows API –Linux: tpm_tools, GUI TPMManager | PV204: Trusted boot 27 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg TPM 1.2 vs. TPM 2.0 | PV204: Trusted boot https://en.wikipedia.org/wiki/Trusted_Platform_Module •TPM 2.0 introduced algorithm flexibility (no fixed SHA-1) –If (some) algorithm is broken, no need to create “TPM 3.0” •TPM 2.0 often supports legacy API 1.2 (switch in BIOS) •TPM 2.0 seems to focus on IoT-like devices (support TLS) 28 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Provided security functions I.“Measured” boot with remote attestation –Provide signed log of what executed on platform (PCR) II.Storage of keys (disk encryption, private keys…) –Can be additionally password protected III.Binding and Sealing of data –Encryption key wrapped by concrete TPM’s public key IV.Platform integrity –Software will not start if current PCR value is not right | PV204: Trusted boot 29 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg TPM Trusted Software Stack stack | PV204: Trusted boot Infineon, http://www.cs.unh.edu/~it666/reading_list/Hardware/tpm_fundamentals.pdf 30 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg TPM PCR •Platform Configuration Register (PCR) •Measurement cumulatively stored in PCR –measurement = SHA1(next block to execute) –PCR[i] = SHA1(PCR[i] | new_measurement) –Current block measure & store next before passing control •PCR cannot be erased until reboot –Every part that was executed is stored –Possible to perform after-the-fact verification what executed •Idea: boot what you want, but PCR will hold trace •Multiple PCRs to support finer grained reporting | PV204: Trusted boot 31 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Platform attestation – PCR registers •W: PCPTool.exe GetPCRs •L: cat `find /sys/class/ -name "tpm0"`/device/pcrs | PV204: Trusted boot 32 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Remote attestation of platform state •So you measured your boot. How to prove your state to remote party? • •Idea: 1.Take PCR values (inside TPM) 2.Sign it (inside TPM) by TPM’s private key (AIK) 3.Remote party holds public key and can verify signature => trust in authenticity of PCR values | PV204: Trusted boot D:\Documents\Obrazky\question.png 33 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Remote attestation of platform state •Apps running on your computer measured in PCRs •Your TPM contains unique Endorsement key •You can generate Attestation key inside TPM (AIK) –And sign AIK by Endorsement key (inside TPM) •You can sign your PCRs by AIK (inside TPM) •Remote party can verify signature on AIK key –Using public key of Endorsement key •Remote party can verify signature on PCRs –Using public key of AIK key •Remote party now knows “what” you are running • | PV204: Trusted boot 34 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Remote attestation •Multiple PCRs to support finer grained reporting –not just single cumulative value •Multiple PCRs available –BIOS, ROM, Memory Block Register [index 0-4] –OS loaders [5-7], Operating System [8-15] –Debug [16], Localities, Trusted OS [17-22] –Application specific [23] •What is PCR measurement good for? –PCR content can be signed by TPM’s private key and exported –List of applications claimed to be executed (=> PCR expected value can be recomputed by remote party) –=> Remote attestation – • | PV204: Trusted boot 35 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Platform attestation – PCR registers • | PV204: Trusted boot PADS TPM_VERSION_12 28 8cb1a2e093cf41c1a726bab3e10bc1750180bbc5 b2a83b0ebf2f8374299a5b2bdfc31ea955ad7236 b2a83b0ebf2f8374299a5b2bdfc31ea955ad7236 b2a83b0ebf2f8374299a5b2bdfc31ea955ad7236 68fffb7e5c5f6e6461b3527a0694f41ebd07e4e1 8e33d52190def152c9939e9dd9b0ea84da25d29b b2a83b0ebf2f8374299a5b2bdfc31ea955ad7236 b2a83b0ebf2f8374299a5b2bdfc31ea955ad7236 0000000000000000000000000000000000000000 0000000000000000000000000000000000000000 0000000000000000000000000000000000000000 b2a83b0ebf2f8374299a5b2bdfc31ea955ad7236 7c84e69cd581eefd7ebe1406666711fd4fda8aa8 01788a8a31f2dafcd9fe58c5a11701e187687d49 26cda47f1db41bedc2c2b1e6c91311c98b4e2246 0000000000000000000000000000000000000000 0000000000000000000000000000000000000000 ffffffffffffffffffffffffffffffffffffffff ffffffffffffffffffffffffffffffffffffffff ffffffffffffffffffffffffffffffffffffffff ffffffffffffffffffffffffffffffffffffffff ffffffffffffffffffffffffffffffffffffffff ffffffffffffffffffffffffffffffffffffffff 0000000000000000000000000000000000000000 … 36 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg TPM platform info •Provides information about your platform state •Included in PCR12 (Operating System information) – • • • • • • • • | PV204: Trusted boot 44 2 0 66 179136858 0 64 179136858 45 0 0 67 179136858 0 67 179136858 Reboot => 37 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg TRUSTED BOOT – REAL IMPLEMENTATIONS • | PV204: Trusted boot 38 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Verified boot - Chromium OS •Starts with read-only part of firmware/BIOS (root of trust) –Cannot be forged, but also cannot be not updated –Contains permanently stored root RSA public key •“Verified” boot strategy is used –Verifies that all executed code is from Chromium OS source tree –Code signatures verified by (shorter) keys signed by root key •speed tradeoff + possibility to update compromised keys •Does not completely prevent user to boot other OSes –Developer mode turned on => signature on kernel not checked –TPM is used to provide mode reporting (normal/devel/recovery) •https://www.chromium.org/chromium-os/chromiumos-design-docs/verified-boot •https://www.chromium.org/chromium-os/chromiumos-design-docs/verified-boot-crypto | PV204: Trusted boot 39 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Chromium OS uses of TPM •Limited remote attestation (PCR[0] used) –to store developer and recovery mode switches •Prevent rollback attack –Prevented by strictly increasing version of key & firmware –Version is written in TPM’s NV RAM location, only read-only firmware can update this location –Key version prevents update to older (compromised) key –Firmware version prevents update to vulnerable firmware •Store selected user’s private keys (secure storage) •Wrap selected disk encryption keys by TPM’s system key •https://www.chromium.org/developers/design-documents/tpm-usage • | PV204: Trusted boot 40 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg UEFI SECURE BOOT •Secured and Trusted Boot | PV204: Trusted boot 41 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg UEFI secure boot principles •Platform key (RSA 2048b, PK) for authentication of platform owner •Key exchange keys (KEKs) for authentication of other components (drivers, OS components…) 1.“Setup" mode – platform key (PK) is not loaded yet –Everybody can write its own platform key (become owner) –Once PK is written, switch to “user” mode 2.“User” mode –New keys (PKs, KEKs) can be written only if signed by PK –New software components loaded only if signed by KEKs – | PV204: Trusted boot 42 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg • | PV204: Trusted boot The potential boot process from system power on for a conventional BIOS system Microsoft, Secured Boot and Measured Boot: Hardening Early Boot Components Against Malware 43 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg • | PV204: Trusted boot Diagram illustrating the potential measured boot process for UEFI platforms 44 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg WINDOWS 8/10 TRUSTED BOOT •Secured and Trusted Boot | PV204: Trusted boot 45 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg D:\Documents\Obrázky\bootProcess.png Windows 8/10 trusted boot •Certified Windows 8/10 devices have trusted boot by default –“Verified” boot used (UEFI+OS sign) –“Measured” boot used (TPM) •TPM PCRs used for measurements •TPM used for keys protection –Bitlocker disk encryption key –ROCA relevant CVE-2017-15361 •If Infineon TPM used, patch! • • • • | PV204: Trusted boot D:\Documents\Obrázky\368px-Uefi_logo.svg.png 46 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Windows 8/10 – secure boot process •Certified Windows 8/10 devices must have secure boot enabled by default • • | PV204: Trusted boot Microsoft, Secured Boot and Measured Boot: Hardening Early Boot Components Against Malware 47 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg TPM owner password •You “own” TPM if you can set owner password –One owner password per single TPM •Password set during TPM initialization phase –can be repeated, but content is erased •Password protected storage of keys (Bitlocker…) – | PV204: Trusted boot 48 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg • | PV204: Trusted boot 49 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg BASIC COMPONENTS • | PV204: Trusted boot 50 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg TPM keys •Endorsement key (EK) –Generated during manufacturing, permanent –Remain in TPM device during whole chip lifetime •TPM Storage Root Key (SRK) –Generated by use after taking ownership –New Storage root key can be generated after TPM clear –Used to protect TPM keys created by application •Various delegate keys –Separate keys signed/wrapped by EK, SRK… –Application can generate and store own keys –Good practice: not to have single key for everything – – | PV204: Trusted boot 51 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg TPM storage keys | PV204: Trusted boot •Application keys encrypted under SRK •Exported as protected blob •Stored on mass-storage •If needed, decrypted back and placed into slot •Key usable until removed – – http://www.cs.unh.edu/~it666/reading_list/Hardware/tpm_fundamentals.pdf 52 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg TPM policy •TPM releases secret only when PCR contains particular value •Enforcement even in measured-only mode –Key is not released if unexpected component was started (started => is included in measurements) •Conditions can use ANDs and ORs •How to handle policy updates? –Change policy of state only from already valid state – | PV204: Trusted boot 53 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Programming with TPM •TPM Platform Crypto-Provider Toolkit –https://research.microsoft.com/en-us/downloads/74c45746-24ad-4cb7-ba4b-0c6df2f92d5d/ –Source code examples for Attestation and Trusted boot •The TPM Software Stack from Microsoft Research (Java, C#) –https://github.com/Microsoft/TSS.MSR •Measured Boot Tool –https://mbt.codeplex.com/, List of most important functions, example code –Demonstrates TPM secure boot and remote attestation on Windows 8/10 •TrouSerS: open-source stack for TCG –Linux version (2008) •http://trousers.sourceforge.net/ •https://sourceforge.net/projects/trousers/files/tpm-tools/ –Windows port (2010) •http://security.polito.it/trusted-computing/trousers-for-windows/ – | PV204: Trusted boot 54 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg D:\Documents\Obrazky\TPM_cloud_domc.png Usage of TPM in cloud-computing •Combination of virtualization and trusted computing •Modified Xen hypervisor used to make standard TPM available for secret-less virtual machine •Results in significant decrease in the size of trusted computational base (TCB) • | PV204: Trusted boot http://bleikertz.com/research/acns2013.pdf 55 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg DYNAMIC ROOT OF TRUST • | PV204: Trusted boot 56 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Static Root of Trust Measurement (SRTM) •Start trusted immutable piece of firmware –E.g., BIOS loader or Intel Boot Guard •Initiates measurement process –Integrity of every next component is added to TPM’s PCRs –Start ® BIOS ® PCI EEPROM ® MBR ® OS … •But do we need to start only after reboot? –Takes relatively long time –Can we execute the same process, but dynamically? –Can we exclude long chain (BIOS, PCI…)? •Long chain => large Trusted Computing Base (TCB)! – | PV204: Trusted boot 57 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Dynamic Root Trust Measurement (DRTM) •Launch of measured environment at any time –“Late lunch” option –No need to reset whole platform –Can be also terminated after some time •Measurement process similar to static root of trust –Application trust chain executed from dynamic root •Implementation of DRTM –Intel’s TXT (not used much in practice) –Intel’s SGX (all Skylake processors and newer, from 2015) • • – • • | PV204: Trusted boot 58 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Intel’s Trusted Execution Technology •Intel’s TXT uses a processor-based root of trust –Option given in TCG specifications •Goal: shorten chain of trust –Run specific program in verified/trusted chain without restart •Goal: provide independent root of trust (CPU-based) –Processor isolates memory of Measured Launched Environment (MLE) from other processes •Intel’s TXT still uses TPM to store measurements •http://www.intel.com/content/dam/www/public/us/en/documents/guides/intel-txt-software-development- guide.pdf •Outdated, abounded in favor of SGX | PV204: Trusted boot 59 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Intel’s TXT issues 1.TXT still relies on BIOS provided code (SMM) –TXT-started chain can be compromised by forged BIOS –Hard to patch (design decision, not implementation bug) –Proposed defence by hardening and sandboxing SMM 2.Bugs in TXT implementation –Memory corruption, misconfiguring VT-d … –Can be fixed after discovery 3.Bugs in processing residual state of pre-TXT lunch –Maliciously modified ACPI tables –Can be fixed after discovery – – – | PV204: Trusted boot 60 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg tboot – open-source implementation •Pre-kernel/VMM module •Based on Intel’s Trusted Execution Technology •Performs a measured and verified launch of an OS kernel/VMM •http://sourceforge.net/projects/tboot/ • | PV204: Trusted boot 61 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Intel’s SGX : Security enclave •Intel’s Software Guard Extension (SGX) –New set of CPU instructions intended for future cloud server CPUs •Protection against privileged attacker –Server admin with physical access, privileged malware •Application requests private region of code and data –Security enclave (4KB for heap, stack, code) –Encrypted enclave is stored in main RAM memory, decrypted only inside CPU –Access from outside enclave is prevented on CPU level –Code for enclave is distributed as part of application •Trusted Computing Base significantly limited! J –But proprietary Intel code inside CPU L • | PV204: Trusted boot 62 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Intel’s SGX – some details •EGETKEY instruction generates new enclave key –SGX security version numbers –Device ID (unique number of CPU) –Owner epoch – additional entropy from user •EREPORT instruction generates signed report –Local/remote attestation of target platform •Debugging possible if application opt in •Enclave cannot be emulated by VM • • | PV204: Trusted boot 63 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg SGX hardened password verification | PV204: Trusted boot https://jbp.io/2016/01/17/using-sgx-to-hash-passwords/ 64 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Intel SGX is very active research area •CCS2016, NDSS2017… •Many small enclaves to cover whole program –User-annotated code split into many enclaves (“microns”) •Secure interaction between microns (attest, auth. encryption) –Tor, H2O, FreeTDS and OpenSSL successfully transformed •2685, 154, 473 and 307 LOC changes required respectively •TCB only 20KLOC, PANOPLY specific overhead 24% •Memory randomization of code inside enclave –SGX program modified with custom LLVM compiler –Added in-enclave loader for ASLR & swDEP (2703 LOC) –Code&data split into 32/64B units randomized separately •Full library OS based on SGX (Haven, Graphene-SGX) – | PV204: Trusted boot 65 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Recent attacks against SGX •SGX is not a silver bullet •Vulnerable to side-channels –Attacker with physical access explicitly excluded from attacker model –Impacted by Spectre attack (2017) •https://github.com/lsds/spectre-attack-sgx •https://github.com/osusecLab/SgxPectre •Bugs of enclave code are still problem (developer) •Not everything is running inside enclave (other code, user input…) 66 | PV204: Trusted boot P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Programming with Intel’s SGX •Intel SGX SDK –https://software.intel.com/en-us/sgx-sdk –6th generation core processor (or later) based platform with SGX enabled BIOS support •Example: Hardened password hashing –https://jbp.io/2016/01/17/using-sgx-to-hash-passwords/ –https://github.com/ctz/sgx-pwenclave •More SGX info –http://theinvisiblethings.blogspot.cz/2013/08/thoughts-on-intels-upcoming-software.html –http://theinvisiblethings.blogspot.cz/2013/09/thoughts-on-intels-upcoming-software.html | PV204: Trusted boot 67 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg TRUSTED COMPUTING - CRITIQUE • | PV204: Trusted boot 68 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Trusted computing - controversy •For whom is your computed trusted? –Secure against you as an owner? •Is TC preventing users to run code of their choice? –Custom OS distribution? –Open OEM system – locked on first installation –Physical switch to unlock later •Why some people from Trusted Computing consortium think that Trustworthy Computing might be better title? | PV204: Trusted boot 69 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Trusted computing - controversy •R. Anderson, `Trusted Computing' FAQ (2003) –http://www.cl.cam.ac.uk/~rja14/tcpa-faq.html •J. Edge, UEFI and "secure boot“ –http://lwn.net/Articles/447381/ •R. Stallman, Can You Trust Your Computer? –https://www.gnu.org/philosophy/can-you-trust.html •Selected problems addressed in current designs – • • | PV204: Trusted boot 70 P:\CRCS\2012_0178_Redesign_loga_a_JVS\PPT_prezentace\sablona\pracovni\normalni.jpg Summary •Two principal solutions for trusted boot –Verified boot (signatures) and Measured boot (PCR+RA) •Start from clean (and trusted) point –Allow only intended software to run –Or prove what actually executed •Additional hardware inside motherboard / CPU provides wide range of new possibilities (TPM) •Size of Trusted Computing Base matters (TPM/SGX) •Controversy about implication of trusted boot –Who owns and control target platform | PV204: Trusted boot 71